NO. 8 UPPER EOCENE ARTIODACTYLA — GAZIN 43 



and in size is quite appropriate to occlude with the known lower molars 

 of Helohyus lentus. In consequence of this, P. aberrans should be re- 

 garded as a synonym of H. lentus. 



As for P. vagus, the locality data for the "P. aberrans" tooth are 

 confused but would appear to be Washakie Basin, and in all prob- 

 ability Washakie A. 



MEASUREMENTS IN MnXIMETERS OF DENTITION IN TYPE SPECIMEN OF 



Parahyus vagus, y.p.m. no. 10972 



Length of cheek tooth series, anterior margin of alveolus for P2 to 



posterior margin of M3 135.0a 



Premolar series, anterior margin of alveolus for P2 to posterior 



margin of P4 6i.oa 



Molar series, M1-M3, inclusive 75.0 



Ps, anteroposterior diameter : greatest transverse diameter 19.0a: 9.7 



P4, anteroposterior diameter : greatest transverse diameter 26.0 : 12.8 



Ml, anteroposterior diameter : transverse diameter of talonid 19.3 : 13.0 



Ma, anteroposterior diameter : transverse diameter of talonid 21. i : 14.8 



M3, anteroposterior diameter : transverse diameter of trigonid 34.8 : 17.0 



a. Approximate. 



Family HYPERTRAGULIDAE Cope, 1879 



Subfamily Hypertragulinae Matthew, 1908 



Consideration of the form Simhneryx Stock, which appears rather 

 certainly to be a true hypertragulid, evidently related to the Oligocene 

 genus Hypertragulus, suggests possible diverse origins for the groups 

 now united in this family. The antecedents of the Duchesnean Simi- 

 meryx would appear to be in a dichobunid of the type exemplified by 

 Mesomeryx, whereas the leptotragulids, more highly specialized in 

 selenodont development at an earlier date than Simimeryx, were likely 

 derived from a separate portion of the dichobunid stock. This may 

 also be true of the leptomerycines. The rather strong implication for 

 a polyphyletic origin introduces problems in the supergeneric arrange- 

 ment, so that the Hypertragulidae as currently constituted appears 

 unnatural. I do not propose to raise all tribes or subfamilies to full 

 family rank, as I have not been able to determine the extent to which 

 these groups are independent. Perhaps the only forms that should 

 be retained in the Hypertragulidae are the hypertragulids sensu stricto, 

 Simimeryx, and possibly Hypisodus as it seems closer to Hypertragu- 

 lus than to any of the other Oligocene forms. On the other hand, there 

 is a suggestion that the leptotragulids and leptomerycines form a 



